Steam has been used in many different methods for the recovery of oil from subterranean, viscous oil-containing formations. The two most basic processes using steam for the recovery of oil includes a "steam drive" process and "huff and puff" steam processes. Steam drive involves injecting steam through an injection well into a formation. Upon entering the formation, heat transferred to the formation by the steam lowers the viscosity of the formation oil, thereby improving its mobility. In addition, continued injection of steam provides a drive to displace the oil toward a production well from which it is produced. "Huff and puff" processes involves injecting steam into a formation through a well, stopping the injection of steam, permitting the formation to soak and then back producing oil through the original well.
Steamflooding a multi-sand reservoir suffers from poor vertical sweep efficiency caused by unequal steam distribution in the injection wellbore. While establishment of thermal communication between injector and producer is a necessary step for a successful steamflood, such a communication usually develops in a limited number of sands containing oil. With continuing steam injection, the sands in thermal communication tend to receive a majority of the steam, which leads to an increase in its steam/gas saturation. As a result, pressure drop between injector and producer wells become very small. This pressure drop occurs because steamed-out sand acts as a thief zone. With such a small pressure differential, little or no steam is directed to the other target sand layers.
MacBean in U.S. Pat. No. 3,771,598 which issued on Nov. 13, 1973 teaches a method for producing hydrocarbons from a subterranean formation penetrated by an injection well and at least one production well. In this method a mobilizing fluid such as steam was injected through said injection well and into the formation. Steam injection was continued at a pressure level and for a time sufficient to cause breakthrough of the mobilizing fluid through said formation to at leas one production well. Afterwards, the pressure was increased in the productive interval of a formation adjacent said production well after breakthrough had occurred by injecting another fluid down the production well while continuing injection of mobilizing fluid into said formation. Thereafter, hydrocarbons were produced from the formation while maintaining the increased pressure in the formation.
Bombardieri in U.S. Pat. No. 4,130,163 which issued on Dec. 19, 1978 teaches a process for recovering hydrocarbons from a subterranean hydrocarbon-bearing formation which is penetrated by at least two wells having a communicating relationship. A heated fluid is injected into the formation at relatively high pressures by means of both wells for a relatively short period of time, sufficient to fluidize hydrocarbons therein and produce hydrocarbons upon cessation of said injection, but insufficient to result in fluid breakthrough. Next one well is shut in and hydrocarbons are recovered from the formation via the other well. A minimum production rate is selected for the other well whereby a relatively long production span is established. The production rate of the hydrocarbon from the other well is monitored. Afterwards, the production rate declines to the minimum rate, along with reduced temperatures of the produced fluids and additional heated fluid is injected into one well at relatively low pressures over a relatively long time. The objective was to create a driving force into the formation by means of one well and continue production of hydrocarbons from the other well while continuing said fluid drive but without breakthrough. None of the prior art methods solved the problem of removing hydrocarbons during the steam flood from a multiple-sand reservoir which suffers from poor vertical sweep efficiency caused by unequal steam distribution in the injection well.
Therefore, what is needed is a method for equal steam distribution in an injection well to remove hydrocarbonaceous fluid from a multi-sand reservoir which will improve vertical sweep efficiency.